Mr Cameron argued that adding more state borrowing and spending to ease the "cost-of-living crisis" would risk putting the UK on the economic trajectory of Greece.

"It's all sticking plasters and quick fixes cobbled together for the TV cameras - Red Ed and his Blue Peter economy, " said the prime minister.

Earlier in the week, Chancellor George Osborne announced plans to make the long-term unemployed undertake work placements if they want to continue receiving benefits.

In his speech, Mr Cameron did not make any specific policy announcements, but suggested his party was looking at further changes to the welfare system to include in its manifesto for the 2015 general election.

It was wrong that young people could "choose the dole" and right to "offer them something better".

Mr Cameron added: "And let no one paint ideas like this as callous.

"Think about it: with your children, would you dream of just leaving them to their own devices, not getting a job, not training, nothing?

"No - you'd nag and push and guide and do anything to get them on their way… and so must we. So this is what we want to see: everyone under 25 - earning or learning."

'Stand tall'

Mr Cameron, who did not repeat previous no-notes speeches, often looked straight into the lens of the TV camera to address directly the audience outside the Manchester conference centre.

The BBC's chief political correspondent Norman Smith said it was a surprisingly sober speech in parts, with Mr Cameron stressing there was still much work to do to fix Britain's economy.

It was not enough just to clean up Labour's "mess" and pay off the deficit, he wanted to "build something better in its place".

He added: "In place of the casino economy, one where people who work hard can actually get on; in place of the welfare society, one where no individual is written off; in place of the broken education system, one that gives every child the chance to rise up and succeed."

Mr Cameron invoked the spirit of his predecessor Margaret Thatcher, the winner of three general elections, who died earlier this year, saying she had "made our country stand tall again, at home and abroad".

He also made efforts to distance his party, and himself, from the Liberal Democrats, with whom the Tories have ruled in coalition for more than three years.

He promised: "When the election comes, we won't be campaigning for a coalition, we will be fighting heart and soul for a majority Conservative government - because that is what our country needs...

"This party at its heart is about big people, strong communities, responsible businesses, a bigger society - not a bigger state."

'Strong message'

To cheers, Mr Cameron attacked the Lib Dems for "trying to take all the credit" for lowering the minimum earnings threshold at which people start paying income tax.

Labour want the choice at the 2015 general election to be between which party can best help voters with the cost of living. Today the prime minister challenged that analysis

The Lib Dems said they, not the Conservatives, had made a manifesto commitment in 2010 to raise the level at which people start paying tax to £10,000.

And UKIP leader Nigel Farage said the pro-business message conflicted with the reality that membership of the EU was costing the UK "billions in red tape and direct payments from high taxes".

But there was a more favourable response from business groups, with CBI director-general John Cridland saying the prime minister had "sent out a strong message about how vital British business is to the future prosperity of people across the UK".

Simon Walker, director-general of the Institute of Directors also welcomed the speech, but warned that firms would "be looking for him to match the sentiment with action - if tax cuts aren't dirty, let's have a few more of them".